EP1897218B1 - Variable gain amplifier with temperatore compensation and gain linearity enhancement - Google Patents
Variable gain amplifier with temperatore compensation and gain linearity enhancement Download PDFInfo
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- EP1897218B1 EP1897218B1 EP06773601A EP06773601A EP1897218B1 EP 1897218 B1 EP1897218 B1 EP 1897218B1 EP 06773601 A EP06773601 A EP 06773601A EP 06773601 A EP06773601 A EP 06773601A EP 1897218 B1 EP1897218 B1 EP 1897218B1
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- 238000003199 nucleic acid amplification method Methods 0.000 description 3
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G1/00—Details of arrangements for controlling amplification
- H03G1/0005—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal
- H03G1/0017—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal the device being at least one of the amplifying solid state elements of the amplifier
- H03G1/0023—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal the device being at least one of the amplifying solid state elements of the amplifier in emitter-coupled or cascode amplifiers
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/32—Modifications of amplifiers to reduce non-linear distortion
- H03F1/3211—Modifications of amplifiers to reduce non-linear distortion in differential amplifiers
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/4508—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using bipolar transistors as the active amplifying circuit
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G1/00—Details of arrangements for controlling amplification
- H03G1/0005—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45286—Indexing scheme relating to differential amplifiers the temperature dependence of a differential amplifier being controlled
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45324—Indexing scheme relating to differential amplifiers the AAC comprising a Darlington transistor circuit
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45352—Indexing scheme relating to differential amplifiers the AAC comprising a combination of a plurality of transistors, e.g. Darlington coupled transistors
Definitions
- the present disclosure relates to a variable gain amplifier, and more particularly to compensation for temperature and linearity in an amplifier with a wide gain control range.
- variable gain amplifier stages are coupled by an attenuation circuit that receives a voltage input to be amplified.
- a control circuit activates each of the variable gain amplifier stages in a seamless manner in accordance with a control signal applied to a voltage control node, while maintaining no more than one of the stages active at any time.
- Each amplifier stage should provide variable gain with accurate linearity over that portion of the control voltage range within which it is operable.
- FIG. 1 illustrates a similar prior art variable gain amplifier.
- Each stage of a wide dynamic range multi-stage variable gain amplifier may comprise a circuit such as shown in Fig. 1 which, for ease of explanation, is designated with "k" character references, representing amplifier stage K.
- the amplifier stage receives an input Vin+, Vin- and provides an output Iout+, Iout-.
- the inputs are applied to emitter follower transistors 20 and 22, which are coupled to ground through respective current sources.
- resistors 24-32 Connected in series between transistor 20 and ground are resistors 24-32, and a current gain control GCk.
- the gain control may be derived from a variable control voltage setting (not shown) in the manner described, for example, in the above-identified Min application.
- resistors 34 - 42 Connected in series between transistor 22 and ground are resistors 34 - 42, and gain control GCk.
- Iout+ and Iout- Connected between Iout+ and Iout- are six differential pairs of transistors.
- the emitters of a first differential pair of transistors 44 and 66 are connected together.
- the emitters of a second differential pair of transistors 46 and 64 are connected together.
- the emitters of a third differential pair of transistors 48 and 62 are connected together.
- the emitters of a fourth differential pair of transistors 50 and 60 are connected together.
- the emitters of a fifth differential pair of transistors 52 and 58 are connected together.
- the emitters of a sixth differential pair of transistors 54 and 56 are connected together.
- In circuit with each of the transistor emitters is a tail current source.
- the base of transistor 44 is connected to the emitter of transistor 20.
- the base of transistor 48 is connected to the junction between resistors 26 and 28.
- the base of transistor 50 is connected to the junction between resistors 28 and 30.
- the base of transistor 52 is connected to the junction between resistors 30 and 32.
- the base of transistor 54 is connected to the junction between resistor 32 and GCk.
- the base of transistor 56 is connected to the emitter of transistor 22.
- the base of transistor 58 is connected to the junction between resistors 34 and 36.
- the base of transistor 60 is connected to the junction between resistors 36 and 38.
- the base of transistor 62 is connected to the junction between resistors 38 and 40.
- the base of transistor 64 is connected to the junction between resistors 40 and 42.
- the base of transistor 66 is connected to the junction between resistor 42 and GCk.
- Transistors 20 and 22 function as a buffer circuit for the voltage input.
- the emitters of these transistors provide versions of the input signal to the bases of the transistors 44 - 66 that are shifted in accordance with the voltage drops across resistors 24 - 42. If the resistances of all resistors are equal (R), an offset voltage exists between the bases of each differential pair of transistors.
- the offset for the first pair is equal to the difference between the buffered input voltage at the base of transistor 44 and the voltage drops across the five resistors 34 through 42, or proportional to 5xR.
- the offsets for the second through sixth pairs are proportional to 3xR, R, R, 3xR and 5xR, respectively.
- the offset for each pair is designated R i , wherein i represents the number of differential pairs.
- I K is the differential tail current
- ⁇ F is the ratio between collector and emitter current of the corresponding transistors
- V T is the thermal voltage
- R i is the resistance offset value for differential pair i.
- the transconductance can be derived by differentiating I out with respect to V in .
- the gain vs gain control current GC is plotted in Fig. 2 .
- the linear-in-dB output vs input relationship is not precise.
- the plot exhibits curvature, the extent of which can be appreciated more clearly in the plot of Fig. 3 .
- Linearity error is plotted over the range of gain control current GC in the diagram of that figure.
- the gain is relatively linear in the central range, of approximately 0.4m to 0.6m, while having increasing error through the range above 0.6m. A need exists for higher accuracy gain control over the extended range.
- the gain control current is normally referenced to a voltage that is temperature-independent.
- transconductance is a function of thermal voltage V T , which varies with temperature.
- V T is an element in the denominator of two portions of the gain equation.
- gain is variable with temperature.
- US Patent No: 5910751A discloses a circuit arrangement and method with temperature dependent signal swing.
- US Patent No: 5742203A discloses a gain-controllable amplifier and receiver.
- US Patent No: 5526058A discloses a video signal adjusting apparatus, a display using the apparatus, and a method of adjusting the display.
- variable gain amplifier of the prior art are fulfilled, at least in part, by a method of controlling a variable gain amplifier composed of a plurality of parallel coupled differential transistor pairs.
- the method comprising: producing a temperature dependent current source in the current path of each differential transistor pair; generating a gain control current corresponding to a desired gain; converting the generated control current to a temperature dependent gain control current source; applying the temperature dependent gain control current source in circuit with control inputs of the transistors of the paired differential transistors; and modifying the temperature dependent gain control current source to compensate for gain non-linearity.
- the temperature dependent gain .. control current source may be modified by introducing an offset as a function of the gain control current.
- Another method of controlling a variable gain amplifier composed of a plurality of parallel coupled differential transistor pairs comprises: producing a temperature dependent current source in the current path of each differential transistor pair; generating a gain control current corresponding to a desired gain; converting the generated control current to a temperature dependent gain control current source; applying the temperature dependent gain control current source in circuit with control inputs of the transistors of the paired differential transistors; and wherein the step of converting comprises: generating a temperature dependent current; and multiplying the control current by the temperature dependent current.
- a variable gain amplifier comprises a plurality of differential transistor pairs coupled in parallel and a temperature compensation circuit, configured to generate the temperature dependent gain control signal.
- Each transistor pair is coupled tc a temperature dependent current source.
- Control inputs of the transistor pairs are coupled to a temperature dependent gain control signal.
- the temperature compensation circuit includes a first transistor having a control terminal coupled to a control current source and to a zero temperature coefficient source.
- the transistor output is coupled to a current source that is proportional to temperature.
- Output of a second transistor is coupled to the current source proportional to temperature. The conduction current of the second transistor is applied as the temperature dependent gain control signal.
- Emitter follower circuits may be coupled, respectively, to the control terminals of the first and second transistors to reduce base current effects.
- Cross-coupled transistors may be coupled between the emitter follower circuits and the control terminals of the first and second transistors to minimize voltage error.
- a voltage offset circuit is coupled between the cross-coupled transistors and a control terminal of the second transistor to compensate for gain non-linearity.
- the control inputs of first transistors of the transistor pairs are coupled to each other in series through respective impedances and to a temperature dependent gain control signal; and control inputs of second transistors of the transistor pairs are coupled to each other in series through respective impedances and to the temperature dependent gain control signal.
- Fig. 1 is a circuit diagram of one stage of a variable gain amplifier known in the prior art.
- Fig. 2 is a plot of gain vs gain control current for the amplifier of Fig. 1 .
- Fig. 3 is a plot of gain linearity error vs gain control current for the amplifier of Fig. 1 .
- Fig. 4 is a diagram of a variable gain amplifier stage in accordance with the present invention.
- Fig. 5 is a circuit diagram of a circuit that may be used to implement the block shown in Fig. 4 .
- Fig. 6 is a circuit diagram of variation of the circuit of Fig. 5 .
- Fig. 7 is a circuit diagram of variation of the circuit of Fig. 6 .
- Fig. 8 is a plot of gain vs gain control current for the amplifier of Fig. 7 .
- Fig.9 is a plot of gain linearity error vs gain control current for the amplifier of Fig. 7 .
- Fig. 4 is a diagram of a variable gain amplifier stage in accordance with the present invention.
- the coupled emitters of each of the six differential transistor pairs are coupled to ground through a tail current source that is proportional to absolute temperature (k*Iptat).
- Buffer transistors 20 and 22 also are each coupled to ground through a current source k*Iptat.
- Gain compensation circuit 70 is coupled to the control inputs of each of the transistors 44-56 of the six differential pairs through the resistor circuit including resistors 24-42.
- Variations of the gain compensation circuit 70 are shown in detail in Figs. 5-7 . These circuits modify the gain control signals that are generated to vary amplifier gain. Temperature compensation is obtained by counteracting the temperature dependent variable V T in the denominators of the two divisional components of the transconductance gain equation (2).
- the numerators contain the temperature dependent components I ptat and GC, whereby the ratios are maintained invariable.
- the gain control current is compensated to be proportional to absolute temperature (PTAT) so that the gain of the variable gain amplifier is independent of the temperature.
- Fig. 5 is a simplified temperature compensation circuit that may be employed in the circuit 70 of Fig. 4 .
- I ctl is a control current source that may be derived from a variable gain control voltage setting and is independent of temperature. Coupled in series between source terminals Vcc and ground are zero-temperature-coefficient dc current sources I ztc and base-emitter connected diode 72.
- Transistor 74 is coupled between Vcc and I ztc .
- transistor 76 and current source I ptat which is proportional to absolute temperature.
- the base of transistor 76 is coupled to the junction between current source I ctl and diode 72.
- Transistor 78 is coupled to current source I ptat .
- the bases of transistors 74 and 78 are coupled to a voltage reference.
- Transistor 78 produces a current source GC that is coupled to the control circuits of the differential transistor pairs of Fig. 4 .
- V be72 , V be74 , V be76 , V be78 are the base emitter voltages of the associated transistors.
- Fig. 6 is a circuit diagram of a variation of the circuit of Fig. 5 that reduces the effects of the base currents by addition of an emitter follower circuit.
- Emitter follower transistors 80 and 82 are each coupled to a current source between the supply terminals Vcc and ground.
- the base of transistor 80 is coupled to the junction between current source I ctl and diode 72.
- the emitter of transistor 80 is coupled to the base of transistor 76.
- the base of transistor 82 is coupled to the voltage reference.
- the emitter of transistor 82 is coupled to the base of transistor 78.
- the emitter followers reduce the effects of the base currents of the transistors 76 and 78 in the circuit of Fig. 5 .
- Fig. 7 is a circuit diagram of a variation of the circuit of Fig. 6 that overcomes this effect.
- Cross-coupled transistors 84 and 86 are placed in the conduction paths, respectively, of transistors 80 and 82. Resistor 88 is coupled in series with transistor 84. The base of transistor 78 is coupled to resistor 88.
- the cross-coupled transistors minimize voltage error, as can be appreciated by the following relationships.
- Vbe ⁇ 72 - Vbe ⁇ 76 Vb ⁇ 76
- Vbe ⁇ 72 - Vb ⁇ 74 Vb ⁇ 76 - Vb ⁇ 78.
- the voltage error induced by the emitter followers caused by large base currents at transistors 76 and 78 is effectively eliminated by the cross-coupled transistors 84 and 86.
- the circuit of Fig. 7 also corrects for the prior art nonlinear-in-dB gain as a function of GC as exemplified in Figs. 2 and 3 . To compensate for the error shown in the range above 0.6m of those plots, more DC current is needed to pull the gain down for the same control current.
- the desired linear curvature is obtained by insertion of resistor 88 and its effect in circuit with the base resistances of transistors 76 and 78.
- Gain linearity is plotted in Fig. 9 . As can be seen from the latter figure, there is substantially no linearity error from a GC of approximately 0.4 mA throughout the remaining range.
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Abstract
Description
- This application contains subject matter related to copending U.S. Application number
US 2006290428 A1 of Min Z. Zou, filed June 27, 2005 . - The present disclosure relates to a variable gain amplifier, and more particularly to compensation for temperature and linearity in an amplifier with a wide gain control range.
- The above described copending patent application describes the need for high accuracy variable gain amplification over wide frequency bandwidths. An implementation is described in which a plurality of variable gain amplifier stages are coupled by an attenuation circuit that receives a voltage input to be amplified. A control circuit activates each of the variable gain amplifier stages in a seamless manner in accordance with a control signal applied to a voltage control node, while maintaining no more than one of the stages active at any time. Each amplifier stage should provide variable gain with accurate linearity over that portion of the control voltage range within which it is operable.
- A known prior art variable gain amplifier circuit is described, for example, in the publication A Power-Efficient, Low-Distortion Variable Gain Amplifier Consisting of Coupled Differential Pairs, by van Lieshout and van de Plassche, IEEE Journal of Solid-State Circuits, Vol. 32, No. 12, December 1997, and in
U.S. patent 5,742,203 to Van DE Plassche et al .Fig. 1 of the present disclosure illustrates a similar prior art variable gain amplifier. Each stage of a wide dynamic range multi-stage variable gain amplifier may comprise a circuit such as shown inFig. 1 which, for ease of explanation, is designated with "k" character references, representing amplifier stage K. - The amplifier stage receives an input Vin+, Vin- and provides an output Iout+, Iout-. The inputs are applied to
emitter follower transistors transistor 20 and ground are resistors 24-32, and a current gain control GCk. The gain control may be derived from a variable control voltage setting (not shown) in the manner described, for example, in the above-identified Min application. Connected in series betweentransistor 22 and ground are resistors 34 - 42, and gain control GCk. - Connected between Iout+ and Iout- are six differential pairs of transistors. The emitters of a first differential pair of
transistors transistors transistors transistors transistors transistors - The base of
transistor 44 is connected to the emitter oftransistor 20.
The base oftransistor 48 is connected to the junction betweenresistors transistor 50 is connected to the junction betweenresistors transistor 52 is connected to the junction betweenresistors transistor 54 is connected to the junction betweenresistor 32 and GCk. The base oftransistor 56 is connected to the emitter oftransistor 22. The base oftransistor 58 is connected to the junction betweenresistors transistor 60 is connected to the junction betweenresistors transistor 62 is connected to the junction betweenresistors transistor 64 is connected to the junction betweenresistors transistor 66 is connected to the junction betweenresistor 42 and GCk. -
Transistors transistor 44 and the voltage drops across the fiveresistors 34 through 42, or proportional to 5xR. The offsets for the second through sixth pairs are proportional to 3xR, R, R, 3xR and 5xR, respectively. The offset for each pair is designated Ri, wherein i represents the number of differential pairs. - With zero gain control currents in the resistor paths, all differential pairs operate without offset and maximum gain is obtained. Increasing the gain control current will produce different offsets across the individual pairs, thereby downwardly adjusting the gain. The gain vs control current is represented by the following relationship:
- The gain vs gain control current GC is plotted in
Fig. 2 . The linear-in-dB output vs input relationship is not precise. The plot exhibits curvature, the extent of which can be appreciated more clearly in the plot ofFig. 3 . Linearity error is plotted over the range of gain control current GC in the diagram of that figure. The gain is relatively linear in the central range, of approximately 0.4m to 0.6m, while having increasing error through the range above 0.6m. A need exists for higher accuracy gain control over the extended range. - The gain control current is normally referenced to a voltage that is temperature-independent. As evident from equation (2), transconductance is a function of thermal voltage VT, which varies with temperature. VT is an element in the denominator of two portions of the gain equation. Thus, in the known amplifier gain stage of
Fig. 1 , gain is variable with temperature. A need exists to compensate for such variability so that the amplifier gain is independent of temperature.
US Patent No: 5910751A discloses a circuit arrangement and method with temperature dependent signal swing.US Patent No: 5742203A discloses a gain-controllable amplifier and receiver.US Patent No: 5526058A discloses a video signal adjusting apparatus, a display using the apparatus, and a method of adjusting the display. - The above described needs of the variable gain amplifier of the prior art are fulfilled, at least in part, by a method of controlling a variable gain amplifier composed of a plurality of parallel coupled differential transistor pairs. The method comprising: producing a temperature dependent current source in the current path of each differential transistor pair; generating a gain control current corresponding to a desired gain; converting the generated control current to a temperature dependent gain control current source; applying the temperature dependent gain control current source in circuit with control inputs of the transistors of the paired differential transistors; and modifying the temperature dependent gain control current source to compensate for gain non-linearity. The temperature dependent gain .. control current source may be modified by introducing an offset as a function of the gain control current. Another method of controlling a variable gain amplifier composed of a plurality of parallel coupled differential transistor pairs comprises: producing a temperature dependent current source in the current path of each differential transistor pair; generating a gain control current corresponding to a desired gain; converting the generated control current to a temperature dependent gain control current source; applying the temperature dependent gain control current source in circuit with control inputs of the transistors of the paired differential transistors; and wherein the step of converting comprises: generating a temperature dependent current; and multiplying the control current by the temperature dependent current.
- In an embodiment of the present disclosure, a variable gain amplifier comprises a plurality of differential transistor pairs coupled in parallel and a temperature compensation circuit, configured to generate the temperature dependent gain control signal. Each transistor pair is coupled tc a temperature dependent current source. Control inputs of the transistor pairs are coupled to a temperature dependent gain control signal. The temperature compensation circuit includes a first transistor having a control terminal coupled to a control current source and to a zero temperature coefficient source. The transistor output is coupled to a current source that is proportional to temperature. Output of a second transistor is coupled to the current source proportional to temperature. The conduction current of the second transistor is applied as the temperature dependent gain control signal.
- Emitter follower circuits may be coupled, respectively, to the control terminals of the first and second transistors to reduce base current effects. Cross-coupled transistors may be coupled between the emitter follower circuits and the control terminals of the first and second transistors to minimize voltage error. Preferably, a voltage offset circuit is coupled between the cross-coupled transistors and a control terminal of the second transistor to compensate for gain non-linearity. In another embodiment, the control inputs of first transistors of the transistor pairs are coupled to each other in series through respective impedances and to a temperature dependent gain control signal; and control inputs of second transistors of the transistor pairs are coupled to each other in series through respective impedances and to the temperature dependent gain control signal.
- Additional advantages will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiments are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
- Implementations of the present invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements.
-
Fig. 1 is a circuit diagram of one stage of a variable gain amplifier known in the prior art. -
Fig. 2 is a plot of gain vs gain control current for the amplifier ofFig. 1 . -
Fig. 3 is a plot of gain linearity error vs gain control current for the amplifier ofFig. 1 . -
Fig. 4 is a diagram of a variable gain amplifier stage in accordance with the present invention. -
Fig. 5 is a circuit diagram of a circuit that may be used to implement the block shown inFig. 4 . -
Fig. 6 is a circuit diagram of variation of the circuit ofFig. 5 . -
Fig. 7 is a circuit diagram of variation of the circuit ofFig. 6 . -
Fig. 8 is a plot of gain vs gain control current for the amplifier ofFig. 7 . -
Fig.9 is a plot of gain linearity error vs gain control current for the amplifier ofFig. 7 . -
Fig. 4 is a diagram of a variable gain amplifier stage in accordance with the present invention. The coupled emitters of each of the six differential transistor pairs are coupled to ground through a tail current source that is proportional to absolute temperature (k*Iptat).Buffer transistors - Variations of the gain compensation circuit 70 are shown in detail in
Figs. 5-7 . These circuits modify the gain control signals that are generated to vary amplifier gain. Temperature compensation is obtained by counteracting the temperature dependent variable VT in the denominators of the two divisional components of the transconductance gain equation (2). The numerators contain the temperature dependent components Iptat and GC, whereby the ratios are maintained invariable. The gain control current is compensated to be proportional to absolute temperature (PTAT) so that the gain of the variable gain amplifier is independent of the temperature. -
Fig. 5 is a simplified temperature compensation circuit that may be employed in the circuit 70 ofFig. 4 . Ictl is a control current source that may be derived from a variable gain control voltage setting and is independent of temperature. Coupled in series between source terminals Vcc and ground are zero-temperature-coefficient dc current sources Iztc and base-emitter connecteddiode 72.Transistor 74 is coupled between Vcc and Iztc. Also coupled between Vcc and ground aretransistor 76 and current source Iptat, which is proportional to absolute temperature. The base oftransistor 76 is coupled to the junction between current source Ictl anddiode 72.Transistor 78 is coupled to current source Iptat. The bases oftransistors Transistor 78 produces a current source GC that is coupled to the control circuits of the differential transistor pairs ofFig. 4 . - If the base current of
transistor 76 is negligible in comparison to the other circuit currents, the voltage difference between thebases transistors diode 72 andtransistor 74. The circuit ofFig. 5 linearly converts the temperature-independent gain control current Ictl to PTAT-dependent current GC with current gain amplification that can be derived as follows:transistor 76 has been neglected on the assumption that Iptat is on the order of Iztc or less. Current will vary from zero to Iptat when the control current Ictl changes from zero to Iztc. - When the current gain amplification is large, the base currents of
transistors transistor 76 is set to Iptat. The GC relationship set forth above will not be held precisely under these extreme conditions.Fig. 6 is a circuit diagram of a variation of the circuit ofFig. 5 that reduces the effects of the base currents by addition of an emitter follower circuit.Emitter follower transistors transistor 80 is coupled to the junction between current source Ictl anddiode 72. The emitter oftransistor 80 is coupled to the base oftransistor 76. The base oftransistor 82 is coupled to the voltage reference. The emitter oftransistor 82 is coupled to the base oftransistor 78. The emitter followers reduce the effects of the base currents of thetransistors Fig. 5 . - The GC relationship is further compromised when Iptat is larger than Iztc. When the level Iptat current is large, for example 3mA in comparison with 100uA Iztc, the base current may be as large as 60µA (β=50). The
emitter followers equation 1, a large error will be produced in GC.Fig. 7 is a circuit diagram of a variation of the circuit ofFig. 6 that overcomes this effect. -
Cross-coupled transistors transistors Resistor 88 is coupled in series withtransistor 84. The base oftransistor 78 is coupled toresistor 88. The cross-coupled transistors minimize voltage error, as can be appreciated by the following relationships. The translinear loop voltage relationship yields the following:transistor 80 conducts the same collector current astransistor 84, andtransistor 82 conducts the same collector current astransistor 86,transistors cross-coupled transistors - The circuit of
Fig. 7 also corrects for the prior art nonlinear-in-dB gain as a function of GC as exemplified inFigs. 2 and 3 . To compensate for the error shown in the range above 0.6m of those plots, more DC current is needed to pull the gain down for the same control current. The desired linear curvature is obtained by insertion ofresistor 88 and its effect in circuit with the base resistances oftransistors Fig. 9 . As can be seen from the latter figure, there is substantially no linearity error from a GC of approximately 0.4 mA throughout the remaining range. - In this disclosure there are shown and described only preferred embodiments of the invention and but a few examples of its versatility. It is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.
Claims (8)
- A variable gain amplifier comprising:a plurality of differential transistor pairs (44 & 66, 46 & 64, 48 & 62, 50 & 60, 52 & 58, 54 & 56) coupled in parallel, wherein
each transistor pair is coupled to a temperature dependent current source (k*Iptat);
control inputs of the transistor pairs are coupled to a temperature dependent gain control signal; anda temperature compensation circuit (70) configured to generate the temperature dependent gain control signal, the temperature compensation circuit comprising:a first transistor (76) having a control terminal coupled to a control current source (IctI) and to a zero temperature coefficient source (Iztc) and an output terminal coupled to a current source proportional to temperature (Iptat); anda second transistor (78) having an output terminal coupled to the current source proportional to temperature (Iptat);wherein the conduction current of the second transistor (78) is applied as the temperature dependent gain control signal. - A variable gain amplifier as recited in claim 1, further comprising emitter follower circuits (80, 82) coupled, respectively, to control terminals of the first and second transistors (76, 78).
- A variable gain amplifier as recited in claim 2, further comprising cross-coupled transistors (84, 86) coupled between the emitter follower circuits (80, 82) and the control terminals of the first and second transistors (76, 78).
- A variable gain amplifier as recited in claim 2, further comprising a voltage offset circuit coupled between the cross-coupled transistors (84, 86) and a control terminal of the second transistor (78).
- A variable gain amplifier as recited in claim 1, wherein:control inputs of first transistors (44, 46, 48, 50, 52, 54) of the transistor pairs are coupled to each other in series through respective impedances and to the temperature dependent gain control signal; andcontrol inputs of second transistors (66, 64, 62, 60, 58, 56) of the transistor pairs are coupled to each other in series through respective impedances and to the temperature dependent gain control signal.
- A method of controlling a variable gain amplifier composed of a plurality of parallel coupled differential transistor pairs (44 & 66, 46 & 64, 48 & 62, 50 & 60, 52 & 58, 54 & 56), the method comprising:producing a temperature dependent current source (Iptat) in the current path of each differential transistor pair;generating a gain control current corresponding to a desired gain;converting the generated control current to a temperature dependent gain control current source; andapplying the temperature dependent gain control current source in circuit with control inputs of the transistors of the paired differential transistors; andmodifying the temperature dependent gain control current source to compensate for gain non-linearity.
- A method as recited in claim 6, wherein the step of modifying comprises introducing an offset as a function of the gain control current.
- A method of controlling a variable gain amplifier composed of a plurality of parallel coupled differential transistor pairs (44 & 66, 46 & 64, 48 & 62, 50 & 60, 52 & 58, 54 & 56), the method composing:producing a temperature dependent current source (Iptat) in the current path of each differential transistor pair;generating a gain control current corresponding to a desired gain;converting the generated control current to a temperature dependent gain control current source; andapplying the temperature dependent gain control current source in circuit with control inputs of the transistors of the paired differential transistors; andwherein the step of converting comprises:generating a temperature dependent current; andmultiplying the control current by the temperature dependent current.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/166,279 US7262661B2 (en) | 2005-06-27 | 2005-06-27 | Variable gain amplifier with temperature compensation and gain linearity enhancement |
PCT/US2006/023941 WO2007002061A1 (en) | 2005-06-27 | 2006-06-20 | Variable gain amplifier with temperature compensation and gain linearity enhancement |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1897218A1 EP1897218A1 (en) | 2008-03-12 |
EP1897218B1 true EP1897218B1 (en) | 2009-01-28 |
Family
ID=36954811
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP06773601A Active EP1897218B1 (en) | 2005-06-27 | 2006-06-20 | Variable gain amplifier with temperatore compensation and gain linearity enhancement |
Country Status (7)
Country | Link |
---|---|
US (1) | US7262661B2 (en) |
EP (1) | EP1897218B1 (en) |
JP (1) | JP2008544725A (en) |
AT (1) | ATE422110T1 (en) |
DE (1) | DE602006005051D1 (en) |
TW (1) | TWI379508B (en) |
WO (1) | WO2007002061A1 (en) |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7317357B1 (en) * | 2006-06-23 | 2008-01-08 | Linear Technology Corporation | High linearity low noise variable gain amplifier with continuous gain control |
KR100995135B1 (en) * | 2007-12-28 | 2010-11-18 | (주)카이로넷 | Temperature compensation circuit |
JP6101581B2 (en) * | 2013-06-28 | 2017-03-22 | 株式会社日立製作所 | Bias circuit |
US10447318B2 (en) | 2017-02-03 | 2019-10-15 | The Regents Of The University Of Michigan | Low power high gain radio frequency amplifier for sensor apparatus |
Family Cites Families (24)
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US4268759A (en) * | 1979-05-21 | 1981-05-19 | Analog Devices, Incorporated | Signal-processing circuitry with intrinsic temperature insensitivity |
US5077541A (en) | 1990-08-14 | 1991-12-31 | Analog Devices, Inc. | Variable-gain amplifier controlled by an analog signal and having a large dynamic range |
JPH06339148A (en) | 1993-03-29 | 1994-12-06 | Hitachi Ltd | Color correction device, picture display device using the correction device, white balance adjustment system consisting of the display device, white balance adjustment method and color adjustment method |
GB9313840D0 (en) | 1993-07-05 | 1993-08-25 | Philips Electronics Uk Ltd | Cascaded amplifier |
DE4329896A1 (en) * | 1993-09-04 | 1995-03-09 | Thomson Brandt Gmbh | Amplifier stage with a dB linear output voltage |
US5432478A (en) | 1994-01-21 | 1995-07-11 | Analog Devices, Inc. | Linear interpolation circuit |
US5481218A (en) * | 1994-09-30 | 1996-01-02 | Telefonaktiebolaget Lm Ericsson | Logarithmic converter |
EP0737381B1 (en) | 1994-10-28 | 2000-09-06 | Koninklijke Philips Electronics N.V. | A gain controllable amplifier, a receiver comprising a gain-controllable amplifier, and a method of controlling signal amplitudes |
US5684431A (en) | 1995-12-13 | 1997-11-04 | Analog Devices | Differential-input single-supply variable gain amplifier having linear-in-dB gain control |
US5910751A (en) | 1997-02-14 | 1999-06-08 | International Business Machines Corporation | Circuit arrangement and method with temperature dependent signal swing |
JP3119215B2 (en) * | 1997-10-14 | 2000-12-18 | 日本電気株式会社 | Differential amplifier |
US6091275A (en) * | 1998-06-02 | 2000-07-18 | Maxim Integrated Products, Inc. | Linear quad variable gain amplifier and method for implementing same |
US6204719B1 (en) | 1999-02-04 | 2001-03-20 | Analog Devices, Inc. | RMS-to-DC converter with balanced multi-tanh triplet squaring cells |
JP3495282B2 (en) * | 1999-02-22 | 2004-02-09 | 株式会社東芝 | Amplifier with temperature compensation |
US6172549B1 (en) | 1999-02-24 | 2001-01-09 | Analog Devices, Inc. | Low supply current RMS-to-DC converter |
US6489849B1 (en) | 1999-12-17 | 2002-12-03 | Analog Devices, Inc. | Interpolator having dual transistor ranks and ratiometric control |
US6437630B1 (en) | 1999-12-28 | 2002-08-20 | Analog Devices, Inc. | RMS-DC converter having gain stages with variable weighting coefficients |
US6429720B1 (en) | 2000-05-12 | 2002-08-06 | Analog Devices, Inc. | RMS-DC converter using a variable gain amplifier to drive a squaring cell |
US6348829B1 (en) | 2000-02-28 | 2002-02-19 | Analog Devices, Inc. | RMS-DC converter having detector cell with dynamically adjustable scaling factor |
JP3852906B2 (en) * | 2000-11-06 | 2006-12-06 | 株式会社東芝 | Temperature compensation circuit and variable gain amplifier circuit |
US6583667B1 (en) | 2001-12-20 | 2003-06-24 | Institute Of Microelectronics | High frequency CMOS differential amplifiers with fully compensated linear-in-dB variable gain characteristic |
JPWO2004032319A1 (en) | 2002-10-04 | 2006-02-02 | 三菱電機株式会社 | Differential amplifier with temperature compensation function |
FI114761B (en) * | 2003-05-26 | 2004-12-15 | Nokia Corp | Temperature compensated amplifier |
US6894564B1 (en) * | 2003-07-07 | 2005-05-17 | Analog Devices, Inc. | Variable-gain amplifier having error amplifier with constant loop gain |
-
2005
- 2005-06-27 US US11/166,279 patent/US7262661B2/en active Active
-
2006
- 2006-06-09 TW TW095120585A patent/TWI379508B/en active
- 2006-06-20 AT AT06773601T patent/ATE422110T1/en not_active IP Right Cessation
- 2006-06-20 WO PCT/US2006/023941 patent/WO2007002061A1/en active Application Filing
- 2006-06-20 JP JP2008519387A patent/JP2008544725A/en active Pending
- 2006-06-20 EP EP06773601A patent/EP1897218B1/en active Active
- 2006-06-20 DE DE602006005051T patent/DE602006005051D1/en active Active
Also Published As
Publication number | Publication date |
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TWI379508B (en) | 2012-12-11 |
EP1897218A1 (en) | 2008-03-12 |
DE602006005051D1 (en) | 2009-03-19 |
ATE422110T1 (en) | 2009-02-15 |
WO2007002061A1 (en) | 2007-01-04 |
TW200713802A (en) | 2007-04-01 |
US20060290428A1 (en) | 2006-12-28 |
US7262661B2 (en) | 2007-08-28 |
JP2008544725A (en) | 2008-12-04 |
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